Anatomy, Embryology, and Ecology of Arachis Hypogea

Abstract

1. Arachis hypogea is a native of Brazil, but its wild ancestor is not known. While it is a member of the Leguminosae, it has not been definitely placed as to its affinities. 2. It is a low annual which, by a lengthening of the internode just below the ovary, pushes its pod below the surface of the soil where the seeds are ripened. 3. The root system is that of the tap root type. Root hairs are of two kinds, normal root tip hairs, and rosettes at the base of the lateral roots. The hairs are so scantily developed in field grown plants that their influence as absorptive organs is negligible. 4. The seed is a straight embryo, and consists of two large cotyledons, a short hypocotyl, and a plumule composed of a terminal and two lateral buds. 5. The mature embryo sac has eight nuclei and numerous starch grains. The antipodals soon disappear. The endosperm nucleus forms numerous free nuclei, which later form a single layer of cells lining the sac. 6. The fertilized egg produces a massive proembryo, which early differentiates into the embryo region and the suspensor. 7. The gynophore has typical stem structure. There is a large pith, about thirteen vascular bundles, both fascicular and interfascicular cambium, and a cortex. It responds to positive geotropism. 8. It grows well and fruits abundantly in hot, relatively dry climates, although the leaves are typically mesophytic with a few xerophytic characters.